Electrodeposition of platinum metals



Patented Mar. 5, 1935 messes ELEQDEPOSITMNQW TAKE aim dson sea a London, M.

land, assignor to The lintctional Nickel @omy, Ina, New York, N. Yr, a corporation I oi Deia No Drawing. Application as s, 1932, I

No.1i2lfl54. Renewed July 24, 934.-

Great Britain Jul! 11, 1931 scum. (or. sea-1) This invention relates to an improved method for the electrodeposition or platinum group metals like palladium and to a bath. for use in carryingoutsaidmethod.- m.

It is well known that heretofore inthe plating 5 or platinum group metals such as palladium, a

I have discovered a method which overcomes the disadvantages of prior procedures and which avoids thenecessity of adding salts or compounds of platinum metals to the plating bath.

It is an object of the present invention to elimi-' hate the need for periodical additions of platinum metal compounds, suchas palladium salts to plating baths by the use of platinum metal anodes like a palladium anode.

' It is a further; object of the invention to pro-f videa bath containing anelectrolyte capable of platinum metal anode at 9.1,

; anodically dissolving rate substantially equal to that at which platinum metal like palladium is deposited cathodically on articles immersed in the electrolyte. 1

It is also within the contemplation orlthe in-j vention to provide an improved method oimaintaining substantially metal (palladium) concentration :offthe electrolytic baths used, while yielding satisfactory and acceptacle deposits of the-platinum metal.

, Otherobjects. and advantages of the invention '40 become apparent from the following description of a preferred procedure of carrying the in- 'vention 'into practice.

Broadly stated I have found that the most advantageous results of the invention are obtained by using an electrolyte containing a complex nitrite of a platinum metal, such as palladonitrite oi an alkali metal or an alkaline earth metal in solution inwater and also containing an alkali or alkaline earth metal halide, like a chloride or constant the: platinum ehlorlde,,treatingthis'withJasolution Y 'Qabout26 of sodiumnitrite which isfa quantity suflicient to 'convert' the palladiunii-iin the solution to palladonitritefboilin'githebromidev oi an alkali metal oralkaline earth metal. The 'palladonitrite o th w o mor el hciiiii ite th hest r be replaced by a mixture or twofor more such halides. The anode, isj eonstitutedroi alplatinum.

metal, such as" a hard 1 rolled. palladiurni sheet which is dissolved lby theaioresaid trolyte. a For the purpose oi giving those skilled in the art a better understanding oi, theflinvention, the

- following description is givenf otl a preferred procedure or carrying theinventioninto practice.

' Forillustration palladium has-been referred, to

as the metal or the platinum group, although it is "to be understood that the lnvention is not" limited thereto.

One method or running a palladium electrolyte which may be described by way of example is as follows: v

About 38 grams or potassium 'palladonitrite' K2Pd(NO2) 4,2H2O, a well known salt of palladium containing 26.36 per cent of palladium by weight, is dissolved in about one literoi hot water and to the solution so obtainedis added about-25 grams of a halide like potassium bromide' f'lhe mixture is boiled and, allowedto cool. to about 40 50 0., which .isa fsiiitable a: I for the subsequent plating operations As another .examp1e,t ne, 1eft; y be madeby takingi'or each liter oi electrolyjtefsired. about 10 sramsor in aqu'a regia', evaporatingthe product with" drochloric acid one ortwo times re acid and to convert theupalladium-j mixture,-di ssolving suiilcient sodium ,chloride to bring the concentration thereot'in the u e:

trolyte to about 25 per literand then making .up the solution-Ito one liter "M ndanao I u metal nitrite r The sodium salts may be replaced by slum or lithium salts or by, for example,

i -wt tions: the process be carried out at from Milt '40" C. with good results.

, or magnesium salts, and the palladium It h b f und th t th p s of p tration may be varied from that set'iorth but with higher palladium concentrationi it preferred to use sodium salts rather than those" of potassium, for example, since the former are more soluble. The halides may be varied in quantity, but it is preferred to keep their concentration between the limits of about 10 to grams per liter.

The anodes are preferably made of hardrolled palladium sheet. Cast palladium anodes are practically as good while soft annealed palladium sheet may also be used. Soft annealed sheets, however, tend to dissolve non-uniformly. giving a much greater quantity of anode sludge than hard rolled or cast material and such sheets are consequently not so economical in use. The anodes should be made of practically pure'metal in order to obtain the best results and tomvent contamination or the electrolyte.

In order to prevent contamination ot'the electrolyte by any anode sludge which may be formed during the process, the anodes may be placed in, for example, unbleached calico bags. The electrolyte should be operated above room tempera-' ture, preferably at temperatures of from 40 degrees to degrees 0., to obtain the best deposits but the solutions work well at higher or lower temperatures than these.

The current density may conveniently be maintained at about 0.1 ampere per square declmeter and at this density the current efilciencies of the anodic and cathodic processes are both very high, being in the order or 95 to 100 per cent. The current density may rise to about 0.5 amperes per square decimeter it desired.

As one example of a method of carrying out the process and as an illustration 0! the high ei'iiciency of the process when the necessary working conditions are observed, the iollowing may be given:

About 400 cubic centimeters oi. a solution containing about 4.25 grams of palladium as sodium palladonitrite and about 10 grams of sodium chloride were prepared. This solution was used for some time for plating a variety of articles. The temperature or the electrolyte was maintained at about 40-50 C. and the anode and cathode current densities were varied from 0.1 to 0.4 amperes per square decimeter. After about 4.62 grams 0! pa adium had been deposited from theelectrolyte the latter was found to contain about 4.26 grams of palladium. From these figures, it is evident. that. the palladium anode had dissolved anodically and had fully maintained,

, and even very; slightly increased, the palladium content of the electrolyte.

., While the process is particularly suitable for the deposition of palladium on silver, it .mayalso be used for the deposition of palladium on surfaces of gold, copper, brass, bronze, palladium, and nickelsilver. Surfaces such as those of nickel, iron, and steel should first be coated with copper or silver or both from a bath of an alkali metal cyanide. 1! base metals such as copper are to be plated and the electrolytes cont i bromides, it is found to be advisable to work at room temperatures, since at a temperature of about 40 C. local action occurs when the base metal is placed in the electrolyte and dark nonadherent deposits are obtained. However, it the base metal is given a preliminary strike 01 palladium from one or the known ammoniacal solu- 1. The method of depositing palladium electrolytically which comprises establishing a bath containing a palladium anode soluble in an electrolyte containing palladonitrite 01 an "alkali" metal, making the article to be plated the oathode, and passing a current through said soluble palladium anode, said electrolyte and said article to be plated whereby palladium metal is electrodeposited on the article to be plated and the electrolyte anodically dissolves the palladium anode during the electrolysis at a rate substantially equal to that at which palladium is deposited cathodically on articles immersed in the electrolyte.

2. The method oi depositing palladium electrolytically which comprises establishing a bath containing a soluble palladium anode and an electrolyte containing palladonitrite of an alkali metal and a halide 01 an "alkali" metal, making the article to be plated the cathode, and passing a current through said soluble palladium anode, said electrolyte and said article to be plated whereby palladium metal is electrodeposited on the article to be plated and the electrolyte anodically dissolves the palladium anode during the electrolysis at a rate substantially equal to that at which palladium is deposited cathodically on articles immersed in the electro- 3. The method of depositing palladium electrolytically which comprises establishing a bath containing a soluble, hard-rolled, palladium sheet anode and an electrolyte containing palladonltrite 01 an alkali metal, making the article to be plated the cathode, and passing a current through said soluble, hard-rolled palladium sheet anode, said electrolyte and said article to be plated whereby palladium metal is electrodeposited on the article to be plated and the electrolyte anodically dissolves the hard-rolled, palladium sheet anode during the electrolysis at a rate substantially equal to that at which hardrolled, palladium sheet is deposited cathodically on articles immersed in the electrolyte.

4. The method of depositing palladium electrolytically which comprises establishing a bath containing 'palladonitrite of an alkali metal, adjusting the concentration of palladonitrite in the electrolyte to give about 10 grams of palladium per liter, making the article to be plated the cathode, and passing a current through said soluble palladium anode, said electrolyte and said article to be plated whereby palladium metal is electrodeposited on the article to be plated and the electrolyte anodically dissolves the palladium anode during the electrolysis at a rate substantially equal to that at which palladium is deode, and passing a current through said soluble palladium anode, said electrolyte and said article to be plated whereby palladium metal is electrodeposited on the article to be plated and the electrolyte anodically dissolves the palladium anode during the electrolysis at a rate substantially equal to that at which palladium is deposited cathoc'ieally on articles immersed in the electrolyte- ALAN RICHARDSON RAPER. 

